Nanostructured Ion‐Exchange Membranes for Fuel Cells: Recent Advances and Perspectives

Abstract

Polymer-based materials with tunable nanoscale structures and associated microenvironments hold great promise as next-generation ion-exchange membranes (IEMs) for acid or alkaline fuel cells. Understanding the relationships between nanostructure, physical and chemical microenvironment, and ion-transport properties are critical to the rational design and development of IEMs. These matters are addressed here by discussing representative and important advances since 2011, with particular emphasis on aromatic-polymer-based nanostructured IEMs, which are broadly divided into nanostructured polymer membranes and nanostructured polymer-filler composite membranes. For each category of membrane, the core factors that influence the physical and chemical microenvironments of the ion nanochannels are summarized. In addition, a brief perspective on the possible future directions of nanostructured IEMs is presented.

Nanotechnology for environmentally sustainable electromobility

“…Carbon nanotubes and graphene also exhibit more environmentally intensive 50,51 profiles and, like other carbon 7 nanostructures, their handling requires more precaution 56 than graphite 57 . The current carbon nanotube synthesis routes are energy intensive [58][59][60] . Even when potential economies of scale are taken into account, energy requirements for the synthesis of carbon nanotubes through chemical vapour deposition, arc discharge, or laser-assisted methods all remain significant 61 , which in turn result in high greenhouse gas emissions 62 .…”

“…However, handling silicon nanoparticles in carbon nanostructures 56,78 and silicon nanowires 79 requires some precaution. The most popular technique used to grow silicon nanowires is chemical vapour deposition 75 , which has moderate to high energy requirements 60,75 . As a result, the synthesis of nanostructured silicon may result in high greenhouse gas emissions 72 .…”

“…The two most promising catalyst support materials that are environmentally beneficial and demonstrate improved technical performance are carbon nanostructures and titanium dioxide, two materials with low environmental intensity in their bulk form 50,51 ( Figure 5). The synthesis methods for the nanomorphologies, however, may potentially have high energy demand 60 , and thereby be detrimental to the overall climate change performance of the manufacturing process. The graphitized carbon-based nanomaterials have enhanced durability under fuel cell operating conditions 29 , which improves the climate change performance of the PEMFC over the lifetime as a counterpoint for the increased synthesis energy.…”

“…Data from carbon black from references 47,50,51,280 ; data from carbon-based nanostructures from references 31,47,50,51,56,60,154,177,[281][282][283][284][285][286][287][288][289][290][291][292] ; data from carbon-based polymer composites from references 47,50,51,56,86,[293][294][295][296] ; data from carbon-based N-, P-, S-doped nanostructures from references 47,50,51,56,66,151,152,154,283,[297][298][299] ; data from carbon-based SnO2, -TiO2 composites from references 47,50,51,56,66,86,...…”

“…These membranes have generally fallen short of the technical goals for PEMFCs for transport applications; they have lower device efficiency due to their lower ionic conductivity, or are unstable and lack the robustness required for an adequate device lifetime relative to Nafion membranes 50,55 . However, as discussed above, their lack of fluorine atoms generally makes these materials less environmentally intensive than fluorinated membranes and modifications such as covalent attachment of proton-conductive compounds, crosslinking and nanostructure are being explored as methods to overcome weaknesses 49,[56][57][58][59][60] . An exception to the technical performance of this category of membranes are phosphoric acid-doped polybenzimidazole-based membranes.…”